Simple bubble levels measure whether a surface is planar or sloped, and allow a carpenter to level the surface (if so desired). A carpenter might also use a laser level to achieve the same result. A simple bubble level or even laser level, however, do not measure angles and pitches.
For angle and pitch measurement of a sloped surface, a carpenter may measure the sides of a triangle and use geometry to measure the slope, or use a right angle square, which is a right angled tool used for measuring angles. This simple tool is like a protractor and measures degrees or pitch, depending on the measurement scale desired. To measure an existing pitch using a right angle square, a user aligns the right angle square to level or vertical and measures the angles like you might do using a protractor. Such alignment to level and measurement, while not impossible, is not always convenient and takes more time than may be necessary.